Astrocytes, glial cells named after their star-like shape are the most abundant cells in the central nervous system. They are crucial regulators of numerous homeostatic functions as well as play a critical role in modulating the synaptic environment and influencing neuronal activity. Together with neuronal cells, they form the tripartite synapse, a concept describing bidirectional communication between astrocytes and neuronal cells. Astrocytes express various transporter proteins in their plasma membrane for neurotransmitter uptake and are also capable of gliotransmitter release themselves. Regulation of dopamine signalling in the brain involves not only neurons but also non-neuronal cells such as astrocytes, however their role in dopamine clearance is underexplored. Understanding the role of astrocytes in dopamine uptake and homeostasis is crucial for developing potential therapeutic strategies for neurological disorders such as Parkinson's disease.
The aim of this dissertation was to investigate the role of astrocytes obtained from neonatal and adult rats in dopamine uptake, focusing on the pharmacokinetic and molecular characteristics of dopamine transport in two distinct brain regions, striatum and cortex. Additionally, we investigated the impact of dopaminergic drugs, primarily apomorphine and haloperidol, on the expression of transporters involved in dopamine uptake in astrocytes.
Experiments were performed using primary astrocyte cultures, cultured from neonatal and adult rat striatum and cortex. The pharmacokinetic characteristics of astrocyte dopamine uptake were assessed using radiolabelled [3H]-dopamine. Astrocyte cultures were subjected to various conditions to assess the temperature-, time-, and concentration-dependence of [3H]-dopamine uptake in the two studied brain regions. Contribution of transporters to astrocyte dopamine uptake such as the high-affinity transporters the dopamine transporter and norepinephrine transporter as well as low-affinity transporters such as organic cation transporters and plasma membrane monoamine transporter was evaluated by various monoamine uptake inhibitors. mRNA expression of transporters was evaluated by quantitative polymerase chain reaction. In addition, we evaluated the effects of apomorphine, haloperidol and L-DOPA on the expression of transporters involved in dopamine uptake in astrocytes by quantitative polymerase chain reaction.
Our findings support the hypotheses that astrocytes play an active role in dopamine clearance and that dopamine uptake is influenced by several factors including temperature, time, concentration, and brain region. Our findings indicate astrocyte dopamine uptake is mediated by both low- and high-affinity carrier systems, which however may not involve the dopamine transporter. We also observed significant changes in dopamine transporter expression in astrocytes in response to dopaminergic agonists and antagonists, specifically apomorphine and haloperidol. These results contribute to a better understanding of the complex regulation of dopaminergic signalling and provide insights into potential therapeutic targets for neurological disorders.
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